A drum contains forty liters of whisky. Four liters of whisky is taken out and replaced by soda. This process is carried out twice further. How much whisky is now contained by the container?

Suppose a solution contains x units of a whisky from which y units are taken out and replaced by soda

After n repeated operations, quantity of pure liquid remaining in solution

⇒ x(1 − y/x)ⁿ = x(1 − y/x)ⁿ units

Where n = number of replacements

So, whisky in the drum now:

⇒ 40 (1 − 4/40)³ = 40(1 − 1/10)³

⇒ 29.16

∴ 29.16 units of whisky is in the container

• In a hotel, the rooms are numbered from 101 to 130 on the first floor, 221 to 260 on the second floor and 306 to 345 on the third floor. In the month of June this year, the room occupancy was 60% on the first floor, 40% on the second floor and 75% on the
• Are all the four friends viz. A, B, C and D who are sitting around a circular table, facing the centre? I) B sits second to right of D. D faces the centre. C sits to immediate right of both B and D. II) A sits to immediate left to B. C is not an immedia
• The letters A, B, C, D, E, F and G not necessarily in that order, stand for seven consecutive integers from 1 to 10, D is 3 less than A, B is the middle term. F is as much less than B as C is greater than D, G is greater than F.
• Two vessels contain mixtures of milk and water in the ratio of 8 : 1 and 1 : 5 respectively. The content of both of these are mixed in a specific ratio into a third vessel. How much mixture must be drawn from the second vessel to fill the third vessel (ca
• A liquid 'P' is $1\frac{3}{7}$ times as heavy as water and water is $1\frac{2}{5}$ times as heavy as another liquid 'Q' The amount of liquid ‘P' that must be added to 7 litres of the liquid ‘Q' so that the mixture may weigh as much as an equal volume of w